The present invention relates, in general, to the field of magnetoresistive ("MR") devices and methods for fabricating the same. More particularly, the present invention relates to a soft adjacent layer biased magnetoresistive sensor and method for fabricating the same incorporating a natural flux closure design utilizing a substantially coplanar permanent magnet thin film stabilization to obviate induced domain walls in the magnetoresistive and soft adjacent layers.
Magnetoresistive sensors, or heads, are known to be useful in reading data from a magnetic media with a sensitivity exceeding that of inductive or thin film heads. In operation, an MR sensor is used to detect magnetic field signal changes from a magnetic media due to the fact that the resistance of the MR sensor changes as a function of the direction and amount of magnetic flux being sensed.
It is also generally known that for an MR sensor to function effectively, it must be subjected to a transverse bias field to linearize its response. The transverse bias field is applied normal to the plane of the magnetic media and parallel to the surface of the MR sensor. Various techniques for effectuating such transverse biasing are presently known including current shunt and soft adjacent layer ("SAL") film biasing, with the latter technique being generally superior for extending the usefulness of MR sensors to storage devices of ever higher areal densities.
It is also known that an MR sensor may be utilized in conjunction with a longitudinal bias field extending parallel to the surface of the magnetic media and parallel to the major axis of the MR sensor. Stabilization of MR sensors by means of a longitudinal bias field is necessary for their application with high track density disk files in order to suppress Barkhausen noise. Barkhausen noise results from unstable magnetic properties such as multi-domain activities within the MR element.
With respect to the application of a longitudinal bias field for the suppression of Barkhausen noise in an MR sensor, the literature describes a number of techniques primarily dealing with "exchange bias" through use of an antiferromagnet coupled in some manner to the MR device. With these exchange bias MR sensors, the materials in general use to form an antiferromagnet, such as manganese and its alloys, are known to be highly reactive and have poor thermal characteristics.
In an attempt to solve the problems inherent with the use of an antiferromagnet to provide longitudinal bias, a number of references currently describe the use of an MR sensor stabilized through the use of permanent magnet films. In general, conventional MR head designs using permanent magnets for Barkhausen noise suppression have been found to be not particularly well suited for use with closely coupled magnetic shielding layers. Moreover, while the use of permanent magnet films to provide longitudinal bias is perhaps the most efficacious technique known, conventional designs nevertheless result in inferior and/or unreliable performance due to the tendency of the flux from the interior ends of the permanent magnet films to nucleate undesired edge domains in both the MR and soft adjacent layer films.
The ultimate effectiveness of a given MR device is very much dependant upon the properties of the design employed, particularly when it is used in conjunction with magnetic shields. In this regard, an especially effective design is disclosed in the aforementioned U.S. patent application Ser. No. 07/975,479 filed Nov. 12, 1992. However, the configuration described may, in some instances, result in the device having an equilibrium with a relatively high energy state and, at numerous realizable states of the device, there exist multiple energy equilibrium states. As a consequence, despite the robustness of the design, the possibility exists that the MR or SAL layers might switch irretrievably into one of the nearby states thus altering the device transfer characteristics and, hence, its operating characteristics. The consequence of such a change could render the device inoperative as an effective data transducer in a particular computer mass storage application.